Cover storage/segment with randomized tests

[petethepig]

storage/segment is an implementation of a segment tree, somewhat similar to this wikipedia definition.

This allows us to very efficiently store and (arguably more importantly) query years of profiling data very quickly. The problem is that operations on this type of data structure are quite complex, and I already found multiple bugs while working on them (most recently this: 47ebbd9).

To give us some more confidence I think we should add some randomized tests where it would randomly "write" a bunch of data to a simple data structure (e.g just an array) and our segment tree. Then it would read the results from the simple data structure + from the segment tree and compare them.

This way we a) might be able to find more subtle bugs, b) prevent regressions

[petethepig]

Fixed in #123